For years UC Berkley accepted affirmative action students with low SAT scores. Their graduation rate was very low. When they changed their admissions standards and only accepted students with better scores the graduation rate greatly improved.
Liberal do-gooders actually hurt the AA admits. They throw these poorly prepared students into classes where they have no chance to succeed. They flunk out and return home as losers. Had they gone to a less selective school they might have done very well.
Agreed. Thomas Sowell has done good work on this.